Sulfonium salt, chemically amplified resist composition, and patterning process

Abstract

A sulfonium salt having both anion and cation moieties in the molecule functions as a photoacid generator and is compatible with other components. A resist composition comprising the sulfonium salt has the advantages of reduced acid diffusion and forms a pattern with a good balance of sensitivity, MEF and DOF, less outgassing, and minimal defects.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2015-107652 filed to in Japan on May 27, 2015, the entire contents of which are hereby incorporated by reference.TECHNICAL FIELD[0002]This invention relates to a sulfonium salt of specific structure, a chemically amplified resist composition comprising the salt, and a pattern forming process using the resist composition.BACKGROUND ART[0003]While a number of recent efforts are being made to achieve a finer pattern rule in the drive for higher integration and operating speeds in LSI devices, DUV and EUV lithography processes are thought to hold particular promise as the next generation in microfabrication technology. In particular, photolithography using an ArF excimer laser as the light source is requisite to the micropatterning technique capable of achieving a feature size of 0.13 μm or less.[0004]The ArF lithography started partial use from ...

AI Technical Summary

Benefits of technology

[0046]The inventive sulfonium salt is fully compatible with resist components and produces less outgassing. When processed by lithography, a chemically amplified resist composition comprising the sulfonium salt forms a pattern with a high sensitivity, improved MEF, improved DOF, and minimal defects.

Problems solved by technology

Although lithography using F2 laser (157 nm) was initially thought promising as the next lithography for 45-nm node devices, its development was retarded by several problems.

These salts generate perfluoroalkanesulfonic acids, especially perflucrooctanesulfonic acid (PFOS), which are considered problematic with respect to their non-degradability. biological concentration and toxicity.

It is rather restricted to apply these salts to the resist material.

Instead, PAGs capable of generating perfluorobutanesulfonic acid are currently used, but are awkward to achieve a high resolution because of substantial diffusion of the generated acid in the resist material.

Despite a reduced degree of fluorine substitution, these PAGs still have the following problems.

Since they do not have a decomposable substituent group such as ester structure, they are unsatisfactory from the aspect of environmental safety due to ease of decomposition.

The molecular design to change the size of alkanesulfonic acid is limited.

Fluorine-containing starting reactants are expensive.

As the circuit line width is reduced, the degradation of contrast by acid diffusion becomes more serious for the resist material.

A low bake temperature, however, inevitably leads to a low sensitivity.

A resist composition comprising this PAG, however, is still insufficient in precise control of acid diffusion, and its lithography performance is unsatisfactory when evaluated totally in terms of MEF, pattern profile and sensitivity.

These defects form because PAG or other resist components have low solubility in casting solvent and leave undissolved residues after developer immersion.

Although the PAG of betaine structure has an acid diffusion suppressing ability and advantages like reduced outgassing, it still suffers from a low solubility in organic solvent and tends to form defects.

However, the RAGS described therein allow for noticeable acid diffusion, and their lithography performance is unsatisfactory to the current requirement to form resist patterns at high resolution.

Images